An internal combustion engine includes a plurality of cylinders formed by an engine block. Each cylinder is capped by a cylinder head, and the cylinders and cylinder head together form a plurality of combustion chambers. Each combustion chamber includes a piston disposed therein. In one example, the internal combustion engine may be supplied with fuel (e.g., gasoline, diesel, etc.) by a plurality of fuel injectors. Each combustion chamber is configured to combust a mixture of fuel and a combustible gas (e.g., air). The combustion chambers receive air via an intake system including one or more intake ports coupled to each combustion chamber. Each intake port includes an intake valve disposed therein. The injected fuel and air may mix and be combusted within each combustion chamber. The resulting gases from combustion may then exit each combustion chamber via an exhaust system including one or more exhaust ports coupled to each combustion chamber, with separate exhaust valves disposed within each exhaust port.
Vehicles including an internal combustion engine configured for direct injection as described above may additionally include an exhaust gas recirculation (EGR) system. The EGR system diverts a portion of the exhaust gases from the exhaust system back to the intake system to cool combustion temperatures and reduce throttling losses, thus improving vehicle emissions and fuel economy. However, in some examples, diluting intake gases with exhaust gases via the EGR system may result in combustion instability and reduced combustion rates.
Attempts to address combustion instability and reduced combustion rates include fluidly coupling each combustion chamber with a separate pre-chamber. One example approach is shown by Attard in U.S. Patent No. 2012/0103302. Therein, an ignition system for an internal combustion engine is disclosed, with the ignition system including a pre-chamber coupled to a combustion chamber and formed within an interior of a cylinder head. The pre-chamber includes a nozzle positioned away from a proximal portion of the pre-chamber. An igniter portion of an ignition device ignites fuel within the pre-chamber, and partially combusted pre-chamber products are forced downward through orifices in the pre-chamber to ignite a main fuel charge within the combustion chamber. Another example approach is shown by Tozzi in U.S. Pat. No. 7,922,551. Therein, a spark plug including a cylindrical shell with a pre-chamber is disclosed, with the cylindrical shell capped by an endcap including a plurality of holes. Combustion of fuel/air may occur within the pre-chamber and a plume of combusted materials from the pre-chamber may ignite fuel/air within a main combustion chamber.
However, the inventors herein have recognized potential issues with such systems. As one example, a geometry of a pre-chamber (such as a pre-chamber formed by a cylindrical shell of a spark plug, or a pre-chamber formed within an interior of a cylinder head) may not be optimized for engine operating conditions in which a relatively large amount of EGR gases are mixed with fresh intake air. For example, although the pre-chamber may be configured to increase a combustibility of an air/fuel mixture by increasing a pressure and temperature of the mixture within the pre-chamber, combusted gases may become trapped within the pre-chamber, thereby inhibiting combustion during subsequent combustion cycles by diluting fresh intake air with the trapped gases within the pre-chamber.
In one example, the issues described above may be addressed by a system comprising: a combustion chamber formed by a cylinder capped by a cylinder head; a pre-chamber formed by the cylinder head, the pre-chamber extending away from the cylinder head and into the cylinder; and a piston disposed within the cylinder, the piston including a protrusion shaped to fit within the pre-chamber. As one example, the pre-chamber includes a plurality of orifices formed by a sidewall of the pre-chamber, and the protrusion of the piston presses into the pre-chamber through a bottom aperture of the pre-chamber. A tip of a first spark plug is disposed within the pre-chamber and may be actuated by a controller to ignite an air/fuel mixture within the pre-chamber. Partially combusted air/fuel mixture may spray outward from the orifices of the pre-chamber and into the combustion chamber, thereby igniting an air/fuel mixture within the combustion chamber. In another example, a spark timing of the pre-chamber may be adjusted by the controller in response to engine operating conditions. By configuring the system in this way, a pressure and temperature of air/fuel mixture within the pre-chamber may be increased, thereby increasing a combustibility of the air/fuel mixture. The combustion of the air/fuel mixture within the pre-chamber may be controlled by adjusting the spark timing within the pre-chamber, and engine performance may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.